1. Field of the Invention
The present invention relates to a method of establishing communications using ultrawideband (UWB) signals.
2. Description of the Prior Art
Wavelet signals are used in the communication art to transmit digital information using modulation, for example pulse position modulation (PPM) or ON-OFF keying (OOK) of the wavelet signals.
Because the energy spectrum of wavelet signals is spread over a very wide frequency band, the global energy level can, all other performance factors being equal, be relatively low, with the result that using wavelet signals makes it easier to conform to the regulations governing telecommunications. Moreover, communication using wavelet signals is relatively insensitive to interference and to reflections, and therefore can be used with advantage in confined environments in which other narrow frequency band high power communications are already present. As a general rule, a UWB signal has a bandwidth BRF such that, at a center frequency fc:
      B    RF    ≥            f      c        4  
Several methods of generating UWB wavelet signals are known in the art. They employ either short Gaussian pulses or bursts or scanning of sinusoidal signals obtained by radio techniques or fast switching (fast on-off keying) techniques.
However, as the duty factor of wavelet signals used for digital communications is relatively low, the prior art methods cited above have the drawback of necessitating synchronization between the transmitter and the receiver, to make the active window of the receiver coincide with wavelets sent by the transmitter. This kind of synchronization requires relatively complex circuits. Moreover, the circuits necessary for generating the wavelets are also relatively complicated.
An object of the invention is to provide a method of establishing ultrawideband communications for transmitting digital information that necessitates only simple circuits that are available off the shelf and dispenses with synchronization between transmission and reception.